关于 SDL_Window 和 unique_ptr 的几个问题 [英] Couple of questions about SDL_Window and unique_ptr

问题描述

我目前在将 SDL_Window 指针存储为 std::unique_ptr 时遇到问题.
我尝试的是:

I currently had a problem with storing a SDL_Window pointer as a std::unique_ptr.
What I tried was:

std::unique_ptr<SDL_Window> window_;

解决办法:

std::unique_ptr<SDL_Window, void(*)(SDL_Window*)> window_;

第一次尝试在内存头中不断抛出错误，说 SDL_Window 是一个不完整的类型.好吧，我知道 SDL_Window 是一个结构体，不能用

The first attempt kept throwing errors in the memory header, saying SDL_Window is an incomplete type. Well I know that SDL_Window is a struct and can't be instanciated with

SDL_Window* window_ = new SDL_Window();

因此实例化是通过 SDL_CreateWindow(params) 完成的.

therefore the instanciation is done with SDL_CreateWindow(params).

问题是:

1. 为什么我不能为 SDL_Window 调用默认构造函数(或任何其他构造函数)?

2. 为什么在这种情况下 unique_ptr 需要删除器，但在这里不需要:

1. Why can't I call the default constructor (or any other) for SDL_Window?

2. Why does the unique_ptr needs a deleter in this case, but not here:

renderSystem_ = std::unique_ptr<Renderer::RenderSystem>(new Renderer::RenderSystem());

RenderSystem 是一个只有默认构造函数和析构函数的类.
是不是因为unique_ptr可以访问析构函数，它充当deleter，不需要作为模板参数进来?

RenderSystem being a class with just a default constructor, destructor.
Is it because the unique_ptr can access the destructor, which acts as the deleter and doesn't need to come as a template argument?

提前致谢！

推荐答案

SDL_Window 类型，正如编译器所说，是不完整的.

The SDL_Window type is, just like the compiler says, incomplete.

SDL 库使用 C 语言中的一种常见模式:指向不完整类型的指针.

The SDL library is using a common pattern in C language: pointers to incomplete type.

在创建唯一指针时，SDL_Window 类型在编译器中看起来像这样:

At the point you create the unique pointer, the SDL_Window type looks to the compiler like this:

struct SDL_Window;

这是创建不完整类型的一种方法.

That's one way you can create an incomplete type.

除了SDL_Window 是一种类型，而不是全局变量或函数之外，编译器一无所知.这也意味着它不能假设它有多大，也不能假设它有任何构造函数或析构函数.

The compiler doesn't know anything except that SDL_Window is a type, and not a global variable or a function. This also means it cannot assume what size it has, it cannot assume that it has any constructors or a destructor.

至于SDL_Window的唯一指针，另一种方法是使用这个:

As for the unique pointer to the SDL_Window, another way is to use this:

struct SDLWindowDestroyer
{
    void operator()(SDL_Window* w) const
    {
        SDL_DestroyWindow(w);
    }
};

std::unique_ptr<SDL_Window, SDLWindowDestroyer> window_;

现在您不需要在构造函数中为 window_

Now you don't need to provide a function in a constructor to the window_

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